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Suchada Rajca - One of the best experts on this subject based on the ideXlab platform.
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cross conjugated oligothiophenes derived from the c2s n helix asymmetric synthesis and structure of carbon sulfur 11 helicene
Journal of the American Chemical Society, 2005Co-Authors: Makoto Miyasaka, Andrzej Rajca, Maren Pink, Suchada RajcaAbstract:(−)-Sparteine-mediated asymmetric synthesis of di-n-octyl-substituted carbon−sulfur [11]helicene, a helical (C2S)n β-undecathiophene, is described. The atom-efficient routes rely on one-step tri-annelation or two-step di- and mono-annelation to provide enantiomeric excess of (+)- or (−)-[11]helicene, respectively. X-ray structures for homologous [11] and [7]helicenes indicate similar helical curvatures. The optical band gap, Eg ≈ 3.5 eV, is estimated for the (C2S)n helix polymer, with onset of electron localization at n ≤ 7.
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cross conjugated oligothiophenes derived from the c2s n helix asymmetric synthesis and structure of carbon sulfur 11 helicene
Journal of the American Chemical Society, 2005Co-Authors: Makoto Miyasaka, Andrzej Rajca, Maren Pink, Suchada RajcaAbstract:(-)-Sparteine-mediated asymmetric synthesis of di-n-octyl-substituted carbon-sulfur [11]helicene, a helical (C2S)n beta-undecathiophene, is described. The atom-efficient routes rely on one-step tri-annelation or two-step di- and mono-annelation to provide enantiomeric excess of (+)- or (-)-[11]helicene, respectively. X-ray structures for homologous [11] and [7]helicenes indicate similar helical curvatures. The optical band gap, Eg approximately 3.5 eV, is estimated for the (C2S)n helix polymer, with onset of electron localization at n
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helically annelated and cross conjugated oligothiophenes asymmetric synthesis resolution and characterization of a carbon sulfur 7 helicene
Journal of the American Chemical Society, 2004Co-Authors: Andrzej Rajca, Maren Pink, Makoto Miyasaka, Hua Wang, Suchada RajcaAbstract:The synthesis and characterization of a novel oligothiophene, in which the thiophene rings are annelated into a [7]helicene with cross-conjugated pi-system, are described. Such [7]helicenes may be viewed as fragments of the unprecedented carbon-sulfur (C(2)S)(n)() helix, possessing sulfur-rich molecular periphery. Racemic synthesis of [7]helicene is based upon iterative alternation of two steps: C-C bond homocouplings between the beta-positions of thiophenes and annelation between the alpha-positions of thiophenes. Asymmetric synthesis is carried out using (-)-sparteine-mediated annelation of the axially chiral bis(aryllithium) with electrophilic sulfur equivalent. Alternatively, enantiomers of the [7]helicene are obtained via resolution using menthol-based chiral siloxanes. Racemic [7]helicene and four other macrocyclic products of the annelation are characterized by X-ray crystallography. One of the solvent polymorphs of the [7]helicene possesses pi-stacked columns of opposite enantiomers and multiple short intermolecular contacts, including both homochiral and heterochiral short S...S contacts, suggesting an effective intermolecular electronic coupling in two-dimensions. The [7]helicene is configurationally stable at room temperature and racemizes at 199 degrees C with a half-time of about 11 h. Selected physicochemical studies (UV-vis absorption, CD, optical rotation, and cyclic voltammetry) of the [7]helicene are described.
Makoto Miyasaka - One of the best experts on this subject based on the ideXlab platform.
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cross conjugated oligothiophenes derived from the c2s n helix asymmetric synthesis and structure of carbon sulfur 11 helicene
Journal of the American Chemical Society, 2005Co-Authors: Makoto Miyasaka, Andrzej Rajca, Maren Pink, Suchada RajcaAbstract:(−)-Sparteine-mediated asymmetric synthesis of di-n-octyl-substituted carbon−sulfur [11]helicene, a helical (C2S)n β-undecathiophene, is described. The atom-efficient routes rely on one-step tri-annelation or two-step di- and mono-annelation to provide enantiomeric excess of (+)- or (−)-[11]helicene, respectively. X-ray structures for homologous [11] and [7]helicenes indicate similar helical curvatures. The optical band gap, Eg ≈ 3.5 eV, is estimated for the (C2S)n helix polymer, with onset of electron localization at n ≤ 7.
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cross conjugated oligothiophenes derived from the c2s n helix asymmetric synthesis and structure of carbon sulfur 11 helicene
Journal of the American Chemical Society, 2005Co-Authors: Makoto Miyasaka, Andrzej Rajca, Maren Pink, Suchada RajcaAbstract:(-)-Sparteine-mediated asymmetric synthesis of di-n-octyl-substituted carbon-sulfur [11]helicene, a helical (C2S)n beta-undecathiophene, is described. The atom-efficient routes rely on one-step tri-annelation or two-step di- and mono-annelation to provide enantiomeric excess of (+)- or (-)-[11]helicene, respectively. X-ray structures for homologous [11] and [7]helicenes indicate similar helical curvatures. The optical band gap, Eg approximately 3.5 eV, is estimated for the (C2S)n helix polymer, with onset of electron localization at n
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helically annelated and cross conjugated oligothiophenes asymmetric synthesis resolution and characterization of a carbon sulfur 7 helicene
Journal of the American Chemical Society, 2004Co-Authors: Andrzej Rajca, Maren Pink, Makoto Miyasaka, Hua Wang, Suchada RajcaAbstract:The synthesis and characterization of a novel oligothiophene, in which the thiophene rings are annelated into a [7]helicene with cross-conjugated pi-system, are described. Such [7]helicenes may be viewed as fragments of the unprecedented carbon-sulfur (C(2)S)(n)() helix, possessing sulfur-rich molecular periphery. Racemic synthesis of [7]helicene is based upon iterative alternation of two steps: C-C bond homocouplings between the beta-positions of thiophenes and annelation between the alpha-positions of thiophenes. Asymmetric synthesis is carried out using (-)-sparteine-mediated annelation of the axially chiral bis(aryllithium) with electrophilic sulfur equivalent. Alternatively, enantiomers of the [7]helicene are obtained via resolution using menthol-based chiral siloxanes. Racemic [7]helicene and four other macrocyclic products of the annelation are characterized by X-ray crystallography. One of the solvent polymorphs of the [7]helicene possesses pi-stacked columns of opposite enantiomers and multiple short intermolecular contacts, including both homochiral and heterochiral short S...S contacts, suggesting an effective intermolecular electronic coupling in two-dimensions. The [7]helicene is configurationally stable at room temperature and racemizes at 199 degrees C with a half-time of about 11 h. Selected physicochemical studies (UV-vis absorption, CD, optical rotation, and cyclic voltammetry) of the [7]helicene are described.
Andrzej Rajca - One of the best experts on this subject based on the ideXlab platform.
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cross conjugated oligothiophenes derived from the c2s n helix asymmetric synthesis and structure of carbon sulfur 11 helicene
Journal of the American Chemical Society, 2005Co-Authors: Makoto Miyasaka, Andrzej Rajca, Maren Pink, Suchada RajcaAbstract:(−)-Sparteine-mediated asymmetric synthesis of di-n-octyl-substituted carbon−sulfur [11]helicene, a helical (C2S)n β-undecathiophene, is described. The atom-efficient routes rely on one-step tri-annelation or two-step di- and mono-annelation to provide enantiomeric excess of (+)- or (−)-[11]helicene, respectively. X-ray structures for homologous [11] and [7]helicenes indicate similar helical curvatures. The optical band gap, Eg ≈ 3.5 eV, is estimated for the (C2S)n helix polymer, with onset of electron localization at n ≤ 7.
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cross conjugated oligothiophenes derived from the c2s n helix asymmetric synthesis and structure of carbon sulfur 11 helicene
Journal of the American Chemical Society, 2005Co-Authors: Makoto Miyasaka, Andrzej Rajca, Maren Pink, Suchada RajcaAbstract:(-)-Sparteine-mediated asymmetric synthesis of di-n-octyl-substituted carbon-sulfur [11]helicene, a helical (C2S)n beta-undecathiophene, is described. The atom-efficient routes rely on one-step tri-annelation or two-step di- and mono-annelation to provide enantiomeric excess of (+)- or (-)-[11]helicene, respectively. X-ray structures for homologous [11] and [7]helicenes indicate similar helical curvatures. The optical band gap, Eg approximately 3.5 eV, is estimated for the (C2S)n helix polymer, with onset of electron localization at n
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helically annelated and cross conjugated oligothiophenes asymmetric synthesis resolution and characterization of a carbon sulfur 7 helicene
Journal of the American Chemical Society, 2004Co-Authors: Andrzej Rajca, Maren Pink, Makoto Miyasaka, Hua Wang, Suchada RajcaAbstract:The synthesis and characterization of a novel oligothiophene, in which the thiophene rings are annelated into a [7]helicene with cross-conjugated pi-system, are described. Such [7]helicenes may be viewed as fragments of the unprecedented carbon-sulfur (C(2)S)(n)() helix, possessing sulfur-rich molecular periphery. Racemic synthesis of [7]helicene is based upon iterative alternation of two steps: C-C bond homocouplings between the beta-positions of thiophenes and annelation between the alpha-positions of thiophenes. Asymmetric synthesis is carried out using (-)-sparteine-mediated annelation of the axially chiral bis(aryllithium) with electrophilic sulfur equivalent. Alternatively, enantiomers of the [7]helicene are obtained via resolution using menthol-based chiral siloxanes. Racemic [7]helicene and four other macrocyclic products of the annelation are characterized by X-ray crystallography. One of the solvent polymorphs of the [7]helicene possesses pi-stacked columns of opposite enantiomers and multiple short intermolecular contacts, including both homochiral and heterochiral short S...S contacts, suggesting an effective intermolecular electronic coupling in two-dimensions. The [7]helicene is configurationally stable at room temperature and racemizes at 199 degrees C with a half-time of about 11 h. Selected physicochemical studies (UV-vis absorption, CD, optical rotation, and cyclic voltammetry) of the [7]helicene are described.
Maren Pink - One of the best experts on this subject based on the ideXlab platform.
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cross conjugated oligothiophenes derived from the c2s n helix asymmetric synthesis and structure of carbon sulfur 11 helicene
Journal of the American Chemical Society, 2005Co-Authors: Makoto Miyasaka, Andrzej Rajca, Maren Pink, Suchada RajcaAbstract:(−)-Sparteine-mediated asymmetric synthesis of di-n-octyl-substituted carbon−sulfur [11]helicene, a helical (C2S)n β-undecathiophene, is described. The atom-efficient routes rely on one-step tri-annelation or two-step di- and mono-annelation to provide enantiomeric excess of (+)- or (−)-[11]helicene, respectively. X-ray structures for homologous [11] and [7]helicenes indicate similar helical curvatures. The optical band gap, Eg ≈ 3.5 eV, is estimated for the (C2S)n helix polymer, with onset of electron localization at n ≤ 7.
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cross conjugated oligothiophenes derived from the c2s n helix asymmetric synthesis and structure of carbon sulfur 11 helicene
Journal of the American Chemical Society, 2005Co-Authors: Makoto Miyasaka, Andrzej Rajca, Maren Pink, Suchada RajcaAbstract:(-)-Sparteine-mediated asymmetric synthesis of di-n-octyl-substituted carbon-sulfur [11]helicene, a helical (C2S)n beta-undecathiophene, is described. The atom-efficient routes rely on one-step tri-annelation or two-step di- and mono-annelation to provide enantiomeric excess of (+)- or (-)-[11]helicene, respectively. X-ray structures for homologous [11] and [7]helicenes indicate similar helical curvatures. The optical band gap, Eg approximately 3.5 eV, is estimated for the (C2S)n helix polymer, with onset of electron localization at n
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helically annelated and cross conjugated oligothiophenes asymmetric synthesis resolution and characterization of a carbon sulfur 7 helicene
Journal of the American Chemical Society, 2004Co-Authors: Andrzej Rajca, Maren Pink, Makoto Miyasaka, Hua Wang, Suchada RajcaAbstract:The synthesis and characterization of a novel oligothiophene, in which the thiophene rings are annelated into a [7]helicene with cross-conjugated pi-system, are described. Such [7]helicenes may be viewed as fragments of the unprecedented carbon-sulfur (C(2)S)(n)() helix, possessing sulfur-rich molecular periphery. Racemic synthesis of [7]helicene is based upon iterative alternation of two steps: C-C bond homocouplings between the beta-positions of thiophenes and annelation between the alpha-positions of thiophenes. Asymmetric synthesis is carried out using (-)-sparteine-mediated annelation of the axially chiral bis(aryllithium) with electrophilic sulfur equivalent. Alternatively, enantiomers of the [7]helicene are obtained via resolution using menthol-based chiral siloxanes. Racemic [7]helicene and four other macrocyclic products of the annelation are characterized by X-ray crystallography. One of the solvent polymorphs of the [7]helicene possesses pi-stacked columns of opposite enantiomers and multiple short intermolecular contacts, including both homochiral and heterochiral short S...S contacts, suggesting an effective intermolecular electronic coupling in two-dimensions. The [7]helicene is configurationally stable at room temperature and racemizes at 199 degrees C with a half-time of about 11 h. Selected physicochemical studies (UV-vis absorption, CD, optical rotation, and cyclic voltammetry) of the [7]helicene are described.
Joseph P. A. Harrity - One of the best experts on this subject based on the ideXlab platform.
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development of a 3 3 approach to tetrahydropyridines and its application in indolizidine alkaloid synthesis
Tetrahedron, 2008Co-Authors: Lisa C Pattenden, Harry Adams, Stephen A Smith, Joseph P. A. HarrityAbstract:Abstract A stepwise [3+3] annelation sequence is described that generates tetrahydropyridines from the corresponding aziridines. The scope of this process is described and its potential for the stereoselective synthesis of indolizidines is highlighted by the synthesis of (−)-monomorine.
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formal synthesis of perhydrohistrionicotoxin via a stepwise 3 3 annelation strategy
Tetrahedron Letters, 2006Co-Authors: Olivier Y Provoost, Simon J Hedley, Andrew J Hazelwood, Joseph P. A. HarrityAbstract:Abstract A formal synthesis of (±)-perhydrohistrionicotoxin is described that includes a highly diastereoselective modified Sharpless aziridination and a stepwise [3+3] annelation reaction for the stereoselective construction of the key spiropiperidine motif.